Multistage electrostatic precipitator

ABSTRACT

COVERS AN ELECTRICAL PRECIPITATOR COMPOSED OF TWO TANDEM ELECTROSTATIC SECTIONS ARRANGED TO ELIMINATE DUST OR DIRT OR ANY FORM OF PARTICULATE MATTER WHICH MAY BE CONVEYED WITH AIR OR GAS OR ANY OTHER FLUID MEDIUM. THE FIRST SECTION MAY INCLUDE ONE OR MORE PAIRS OT POSITIVELY CHARGED VERTICAL PLATES BETWEEN EACH PAIR OF WHICH ARE POSITIONED A PLURALITY OF NEGATIVELY CHARGED VERTICAL WIRES, SO THAT A CORONA DISCHARGE MAY BE DEVELOPED BETWEEN THE VERTICAL WIRES AND THE TWO PARALLEL PLATES OF EACH PAIR. THE SECOND SECTION, WHICH IS CONTIGUOUS OF THE END OF THE FIRST SECTION, INCLUDES A PLURALITY OF GRIDS WHICH ARE PARALLEL TO EACH OTHER, BUT PERPENDICULAR TO THE PLATES OF THE FIRST SECTION. THE FIRST GRID OF THE SECOND SECTION MAY BE CHARGED TO A POSITIVE POTENTIAL, AND THE REMAINING GRIDS ARE ARRANGED IN DIFFERENT CHARGED FORMATIONS SO THAT PARTICLES OR MATTER ENTERING THE SECOND SECTION WILL BE URGED TO TURN BACK SO THAT THE PARTICLES MAY BE COLLECTED AND REMOVED FROM THE FLUID MEDIUM.

J. H. VINCENT MULTISTAGE ELECTROSTATC PRECIPITATOR Nov. 2, 1971 2 Sheets-Sheet l Filed Oct. 24, 1969 Fl-G.

n e w L .il s u D S nu G gos How JAMES H. VINCENT BY FIG.2

Y L )M/LC/ L/ZATTORNEY L Nov. 2, 1971 J. H, VINCENT '11;33'616606 MULTISTAGE ELECTROSTATIC PRECIPIIATOR l Filed Oct. 24, 1969 2 Sheets-Sheet 2 G G G G G G 2| 22 2s 24 25 26 J Z 2 ..4 ..1 negatively 2 5 Z I charged E E E 3 2 i E 2 I dus* particles E Z E Z I U 7 s z s 2 7 7 7 P/M l j J i 2 T 7 Dust Laden ww M, wm g o-D 2 E GOS PL 4 :H2 i132 )2 o. (-4 (-x 7 7 7 7 7 7 6? f A 4 gas flow W20 Wzl w22 5 i e E l A i- 7 7 7 un, P3 .4 e e ,z e E E Z 2 I E E Z i Z I Z E E E 2 5 2 (4') floating grids aKv lsKv 24Kv 32m 40m INVENTOR,

JAMES H. VINCENT BY l ATTORN EY United States Patent @ffice 3,616,606 Patented Nov. 2., 1971 U.S. Cl. 55-131 4 Claims ABSTRACT OF THE DISCLOSURE Covers an electrical precipitator composed of two tandem electrostatic sections arranged to eliminate dust or dirt or any form of particulate matter which may be conveyed with air or gas or any other uid medium. The first section may include one or more pairs of positively charged vertical plates between each pair of which are positioned a plurality of negatively charged vertical wires, so that a corona discharge may be developed between the vertical wires and the two parallel plates of each pair. The second section, which is contiguous to the end of the first section, includes a plurality of grids which are parallel to each other, but perpendicular to the plates of the first section. The first grid of the second section may be charged to a positive potential, and the remaining grids are arranged in different charged formations so that particles of matter entering the second section will be urged to turn back so that the particles may be collected and removed from the fluid medium.

This application is a continuation-in-part of my earlier application entitled Electrostatic Precipitator, which was tiled on Feb. 25, 1969 Ibearing Ser. No. 804,050, and is assigned to the assignee of the present patent application.

This invention relates to electrical precipitators and, more particularly, to apparatus and equipments for the precipitation of dust, dirt or other particulate matter which may be included with or suspended in, a fluid medium such as air or gas.

The prior application, Ser. No. 804,050, discloses arrangements of an electrostatic precipitator for the removal of particulate matter borne by a fluid medium such as air or gas. The electrostatic precipitator of the earlier application embodies two series sections. The rst section embodies one or more pairs of parallel metallic plates and a plurality of conductors which are parallel to each other and aligned between the two parallel plates of each pair so that, upon the application of a sufficient voltage between the parallel plates and the intervening conductors, a corona discharge may be established between the plates of each pair and the several related conductors so that particulate matter transmitted along the path between the two parallel plates of each pair will be deflected toward the two plates. If the several conductors are negatively charged, the particles traversing the path may become negatively charged and, if the plates are positively charged, they will attract the charged particles so that they may be deposited on the parallel plates and then removed. The second section may include two or three parallel grids which are parallel to each other but perpendicular to the plates of the first section and so arranged that an electrostatic field may be established between the adjacent grids. The first grid would normally be brought to substantially the same charge as the plates of the first section, that is, to a positive potential (which may be grounded). The third grid, if a third grid is ernployed, would be charged to the same potential as the Iirst grid, but the second grid would be charged to negative potential. The electrostatic field established between the grids of the second section acts on the particles that leave the first section and repels them so that they may be collected on the grids of the second section so that they may be removed from the system.

Although the arrangements of my earlier application Ser. No. 804,050 embodied two or three grids in the second section, it was found, however, that by increasing the number of grids in the second section, a very substantial improvement in the collection of particulate matter will be achieved. By increasing the number of grids in the second section and applying potentials to those grids in accordance with the present invention, particulate matter entering the second section will be confronted by a series of opposing grids bearing oppositively charged voltages which will act to detain the particulate matter between the grids of the second section for a considerably longer period of time than would be possible with the arrangements of my earlier application. Hence, the network of electrostatic fields established in the second section will have more time to act on the particulate matter, thereby slowing down the particulate matter and sweeping the particulate matter to the collecting grids or boundaries. The material increase in the number of grids serves to engulf the particulate matter in eddies and to considerably increase the number of chances that dust or other particles carried by the gas or other fluid medium will become engaged in the eddy pockets, not only to slow down the particles -but also to remove them from the stream of uid traversing the second section.

4One of the principal objects of the present invention is to improve the operational characteristics of an electrostatic precipitator by including a plurality of charged grids so as to provide more opportunities for defiecting and removing particles of matter that enter the precipitator. Such an arrangement, if added to a conventional precipitator, will improve its efiiciency. When such a multi-grid structure is joined to a conventional rst section, the rst section may be reduced in length so that shorter plates may be employed along with a smaller number of parallel conductors between the plates of the irst section. This, therefore, reduces the cost of the overall precipitator while at the same time achieving at least an equal efiiciency in the removal of particulate matter from the fiuid stream. The term grid, as used herein, refers to any perforated structure which is capable of holding an electrical charge and has one or more apertures, which may or may not be regularly spaced, for transmitting lluid.

This invention will be better understood from the following description and explanation when read in connection with the accompanying drawing in which FIG. l discloses and illustrates a cross section of a dual section electrostatic precipitator embodying a plurality of pairs of oppositely poled grids sequentially arranged in its second section; FIG. 2 illustrates a cross section of another dual section electrostatic precipitator embodying a plurality of grids in the second section to which voltages are applied which increase in magnitude in the downstream path; and FIG. 3 illustrates a cross section of a third dual section arrangement in which the second section embodies two grids which are oppositely poled, between which are interposed a plurality of additional grids, sometimes called floating grids.

Throughout the drawing the same or similar reference characters will be employed to designate the same or similar parts.

Referring to PIG. 1 of the drawing, there is illustrated a dual section electrostatic precipitator in which the first section includes three or more vertical parallel plate conductors such as P-1, P-Z, VP-3, etc., organized as a group or groups and arranged so that a plurality of vertical conductors W-10, W-11, W-12 etc., one of the groups are interposed midway between the plates P-2 and P-3 and a plurality of vertical conductors W-20, W-21, W-22, etc., another of the groups are interposed midway between the vertical plates P-3 and P-4, etc. The second section includes, for illustrative purposes, seven parallel grids G-l to G-7. Plates P-l, P-2, P-3, etc., of the first section may be supplied with substantially equal voltages of the same polarity, for example, positive voltages as shown, while the conductors W-10, W-11, WH12 of one path of the first section and the conductors W-20, W-Zl, W-22 of the other path of the first section have applied thereto negative voltages with respect to the several plates between which the conductors are interposed. It will be apparent that a common source of appropriately high voltage may be so arranged that its positive terminal is connected to the several plates P-l, P2 and P-3 and its negative terminal will be connected to the conductors W-10, W-11, W-12, as well as to conductors W-20, W-21, W-ZZ. The grids G-l to G-7 of the second section are poled so that the same positive voltage will be applied to the alternate grids G1, G-3, G-S and G-7 while the corresponding negative voltage will be applied to the alternate grids G-2 G-4 and G-6. The voltages that may be employed in practice may be 40 or more kilovolts as developed by a D.C. source.

As the stream of gas or other fluid with the accompanying entrained dust, dirt or other particulate matter, which may be obtained from any source of such dust, dirt or particulate matter, such as a gas engine or a smoke stack, or a factory, for example, is impelled by a fan or other blower (not shown), the particulate matter will be driven between the several parallel paths of the first section, one path being provided by plates P-1 and P-2 and another path by plates P-2 and P-3. Any particulate matter not removed by the first or conventional section, will enter the second section which includes the several grids G1 to G-'7 which, as already noted, are equally spaced from each other and are parallel to each other and are also perpendicular to the plates P-l, P-2 and P-3 of the first section.

The electrostatic field in the first section, that is, the electrostatic field between each of the wires W-10, W-11 and W-12 and the adjacent plates P-1 and P-Z and the electrostatic field between the wires W*20, W-21 and W-ZZ and the adjacent plates P-3- and P-4, are substantially perpendicular to the fiow path of the particulate matter transmitted through the first section. On the other hand, the electrostatic field between any pair of adjacent grids G1 and G-2, or G-3 and G-4, etc., of the second section is substantially parallel to the direction of movement of the particulate matter which traverses or escapes from the first section and enters the second section.

In the first section of FIG. l, each conductor such as W- or W-20 serves as a discharge electrode producing a negative corona discharge effect so that the entire space in the region of these various conductors is subjected to the corona field. These negatively charged wires, such as W-10 and W-20, attract many of particles of matter which have positive charges thereon. The positively charged plates P-l, P-2 and P-3 attract and serve as collectors of the negatively charged particles. Hence, a good proporation of the particles, whether negatively charged or positively charged, are attracted to and are deposited on the surfaces of the plates P-1, P-2 and P-3 or on the conductors W-10 to W-12 and W-20 to W-22.

Any of the particles that traverse the first section, because they have not been sufficiently attracted by the positively charged plates or the negatively charged conductors of the first section and, therefore, have not been deposited on the plates or conductors and removed, will enter the second section. The particles entering the second section may contain not only negatively charged particles 4 but also positively charged particles. Both types of particles will be treated by the second section.

Those particles which are negatively charged, upon entry into the second section, will be immediately affected by the positive voltage on the first grid G-1. Those particles collected on the grid G1 will be removed; those that continue through the second section will be substantially unretarded by the negatively charged grid G-Z but will be attracted toward or pass through grid G-3 which is also positively charged. Furthermore, some of those negatively charged particles that traverse grid G-3 will be repelled by grid G-4 and turned back toward grid G-3 where they may be collected and removed. Negatively charged particles traversing grid G-5 will be attracted back toward grid G-5 where they may be collected. And so on, and so on, the operation continues with the remaining downstream grids. Similarly, positively charged particles will be deposited on grids G-2, G-4, and G-6. The overall probability of collection of particles increases with the number of grids employed. Thus, the efficiency of the overall system is materially increased.

Thus, those particles which are positively charged and traverse a negatively poled grid and remain 4unattached will be attracted by succeeding negatively poled grids and repelled by positively poled grids that are expected to turn those particles back to be collected by a prior negatively poled grid. Likewise, negatively charged particles traversing positively charged grids and remaining unattached will be attracted by succeeding positively poled grids and repelled by negatively poled grids that serve to reverse the directional fiow of such particles for collection by positively poled grids. This bi-polar reversing process is a feature of this invention. Additional pairs of oppositely poled grids may be inserted between grids G1 and G-7 to increase the number of chances assigned to the grids to reverse and remove particles whatever their polarity may be.

It will be apparent that the FIG 1 arrangement is capable of acting on and removing, and does remove, bothpositively and negatively charged particles that may be passed by the first section of the precipitator and received by its second section. Moreover, the peak voltage in the second section need not be the same as the voltage in the first section. The voltage applied to the second section may be higher or lower than the voltage applied to the first section as may be desired. The voltages applied to either section may be a steady D.C. or pulsed D.C. as desired. This type of bi-polar arrangement has been found to be quite efficient in removing a very high `percentage of particulate matter which is transmitted through the filter.

Because of the high efficiency of the second section of the electrostatic precipitator of FIG. l, the length of the plates P-l, P-2 and P-3, of the first section and the number of vertical conductors such as W-10 and W-20 in the first section may be reduced. The reduction in the length of the plates and in the number of vertical conductors materially affects the overall length of the equipment as well as the cost of the equipment and its installation and at the same time, there is an improvement in the overall efficiency of the particle collecting features.

FIG. 2 differs from FIG. l in that the' second section embodies a grid G-11 which has the same polarity as the grid G1 of FIG. l, but the succeeding grids G12, G-13, G-14, G-15 and G-16 are all similar in structure to the grids of the second section of FIG. l, but they have applied to them negative voltages which increase in magnitude in the downstream direction. Thus, the voltage on the grid G-12 may be a negative voltage with respect to the positive voltage on grid G-11, while the voltage on grid G-13 may be twice the negative voltage on grid G-12, the negative voltage on grid G-14 may be three times the voltage on grid G-12, and So on. The arrangement of FIG. 2 is especially suitable for removing particulate mat` ter which is negatively charged. In this arrangement the grid G-12, due to its negative applied voltage, will repel negatively charged particles which enter the region between grids G-11 and G-12 and drive them toward the positively charged grid G-11 to be removed. Likewise, negatively charged particles that enter the region between grids G-12 and G-13 will be repelled by the standing voltage on grid G-13 and be driven back toward grid G- 12where they may be removed. And so on. Thus, any particle that survives a particular grid, such as G-12 will be repelled by the succeeding grids G-13, G-14 and so on. The overall collection probability of particles, and the efiiciency of system, increase with the numberof grids employed. Each succeeding grid bears a higher repelling voltagie as indicated, but the effective repellingielectric field remains the same between each successive pair of grids.

Although the arrangement of FIG. 2 hasbeen shown and described as employed essentially for removing negatively charged particles, it will be apparent that by reversing the polarities of the various electrodes, a corresponding effect can be produced with respect to positively charged particles.

The voltages on grids G-12 to G-16 need not be linearly or arithmetically arranged. The voltages may be arranged in any desired voltage escalation, whether linear or nonlinear. Furthermore, negatively poled grids such as G-12 to G-16, may serve to attract and remove some or many of the positively charged particles encountered.

FIG. 3 illustrates a modified form of arrangement in which the grid G-21 of the second section is similar to the grid G-11 of FIG. 2, while the terminal grid G-26 is similar to the grid G-16 of FIG. 2. The intermediate grids G-22, G-23, G-24 and G-25 are floating grids in that no voltage is directly applied thereto, but voltages are induced on the several grids G-22 to GV-25. Assuming that the grids G-21 and G-26 have respective positive and negative applied polarities, and the voltage is, for example, 40 kv., as shown, then the grid G-22 will have induced thereon on 8 kv. voltage of a negative polarity, the' grid G-23 will have a negative 16 kv. induced voltage, and the grids G-24 and G-ZS will have induced negative 24 and 32 kv. voltages, as shown. And so on if additional grids or different applied voltages were employed.

- In the arrangement of FIG. 3, each ngative particle traversing the G-Zl will be deflected by theinduced negative voltage on grid G-ZZ to repel and turn back the negatively charged particle to grid G-21 where it may be collected and removed. Likewise, the increased induced voltages on the remaining downstream grids G-ZZ to G-25 will repel negatively charged particles that reach the regions of the respective grids and deflect and turn back such negatively charged particles to the various grids G- 21 to G-25, which may attract and collect the negatively charged particles and, therefore, remove them from the air stream. Naturally, the number of grids linterposed between the two outer grids G-21 and G-26 may be increased or decreased as desired for increasing or decreasing the trend toward reversing the path of any negatively charged particles to the first grid G-21. It will be apparent, moreover, that the same effect may be produced on positively charged particles by reversing the polarities of the several grids of the second section.

The several arrangements shown and illustrated in the drawing serve to improve the efficiency of collection and elimination of particles passing through the parallel and sequential paths of the electrostatic precipitator. Those particles that reach the second section are slowed down and, at the same time, they are turned around. As the particles are slowed down, there are greater and improved opportunities to cause the particles to turn around and be fed back in the direction of the first grid of the second section so that such particles may be collected and removed. Furthermore, because of the increased efficiency of the second section of the several arrangements of this invention, the first section may be simplified so that smaller components may be employed and the number of conductors reduced, thereby reducing the cost of the overall equipment and improving its operation at the same time. The equipment of this invention may be made suitable for those other purposes for which electrostatic precipitators of the kind herein described are conventionally employed. Naturally, any suitable means for receiving and accumulating particles removed by the various elements of both sections may be employed in the practice of this invention.

Although the elements of the rst section are parallel to each other and the elements of the second section are likewise parallel to each other, their relative directions may be changed over considerable angles within the scope and spirit of this invention. Moreover, although the several elements are shown as linear or are linearly arranged, the various elements may be curved to be spherical or elliptical or of any other desired shape within the scope and spirit of this invent-ion.

While this invention has been shown and described in certain particular arrangements merely for illustration and explanation, it will be apparent that the arrangements and operating features may be arranged in other and widely varied organizations for the purpose of carrying out the generall principles and objectives of the present invention.

What is claimed is:

1. An electrostatic precipitator for operating on a gas upon which electrically charged particles of matter are superimposed and travelling in substantially linear paths, comprising a plurality of apertured grids which are parallel to each other and positioned substantially perpendicular to said paths so that the gas and the particles superimposed thereon travel through the apertures of said grids, means for applying a voltage of one polarity to the first of said grids and for applying to the others of said grids respective voltages of the opposite polarity but of ascending magnitudes corresponding to their spacing from the rst grid, so that particles charged to a polarity opposite to that of the first grid will be deected by said other grids toward the first grid.

2. An electrostatic precipitator according to claim 1, including means for charging the particles to be moved through said grids to a polarity which will be opposite to that applied to the first grid.

3. An electrostatic precipitator according to claim 1, including a corona field generator for polarizing particles which are to traverse the grids.

4. An electrostatic precipitator according to claim 1, in which the voltages of ascending order are linearly related to each other.

References Cited UNITED STATES PATENTS 977,335 11/1910 Schaffner 55-129 1,343,285 6/1920 Schmidt 55-137 X 1,357,466 11/1920 Moller 55-138 X 2,225,677 12/1940 White 55-129 X 2,249,801 7/1941 White 55--138 X 2,589,463 3/1952 Warburton 55-139 X 2,990,912 7/1961 Cole 55-130 3,438,180 4/1969 Klouda 55-131 X 3,446,906 5/ 1969 Zulauf 174-35 DENNIS E. TALBERT, I R., Primary Examiner U.S. Cl. X.R. 

